Street performances have a colorful and diverse history. Many of the ideas we have of theatre are descendant from traveling troupes throughout Europe in various decades of the Middle Ages and Renaissance. This will also include traveling minstrels, jugglers, and the ever popular Punch and Judy.
There are still as many different kinds of street performers today as there were four hundred years ago. How many of them qualify as theatre? To bring up Aristotle's definitions may be a little too strict in this sense, but it's a good starting place. And what performers should we be considering musical, performance art, and theatre?
But whatever the definition is, I know that if you walk through the streets of downtown Chicago, there are some acts that are hard to identify what is going on? Sure street theatre needs to be intriguing in order to stop passersby and engage them in your show, but if you can't figure out what the subject is, most people will keep on walking.